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<li class="navelem"><a class="el" href="../../d9/df8/tutorial_root.html">OpenCV Tutorials</a></li><li class="navelem"><a class="el" href="../../d7/da8/tutorial_table_of_content_imgproc.html">Image Processing (imgproc module)</a></li>  </ul>
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  <div class="headertitle">
<div class="title">Histogram Equalization </div>  </div>
</div><!--header-->
<div class="contents">
<div class="textblock"><p><b>Prev Tutorial:</b> <a class="el" href="../../d4/d61/tutorial_warp_affine.html">Affine Transformations</a></p>
<p><b>Next Tutorial:</b> <a class="el" href="../../d8/dbc/tutorial_histogram_calculation.html">Histogram Calculation</a></p>
<table class="doxtable">
<tr>
<th align="right"></th><th align="left"></th></tr>
<tr>
<td align="right">Original author </td><td align="left">Ana Huamán </td></tr>
<tr>
<td align="right">Compatibility </td><td align="left">OpenCV &gt;= 3.0 </td></tr>
</table>
<h2>Goal </h2>
<p>In this tutorial you will learn:</p>
<ul>
<li>What an image histogram is and why it is useful</li>
<li>To equalize histograms of images by using the OpenCV function <a class="el" href="../../d6/dc7/group__imgproc__hist.html#ga7e54091f0c937d49bf84152a16f76d6e">cv::equalizeHist</a></li>
</ul>
<h2>Theory </h2>
<h3>What is an Image Histogram?</h3>
<ul>
<li>It is a graphical representation of the intensity distribution of an image.</li>
<li>It quantifies the number of pixels for each intensity value considered.</li>
</ul>
<div class="image">
<img src="../../Histogram_Equalization_Theory_0.jpg" alt="Histogram_Equalization_Theory_0.jpg"/>
</div>
<h3>What is Histogram Equalization?</h3>
<ul>
<li>It is a method that improves the contrast in an image, in order to stretch out the intensity range (see also the corresponding <a href="https://en.wikipedia.org/wiki/Histogram_equalization">Wikipedia entry</a>).</li>
<li>To make it clearer, from the image above, you can see that the pixels seem clustered around the middle of the available range of intensities. What Histogram Equalization does is to <em>stretch out</em> this range. Take a look at the figure below: The green circles indicate the <em>underpopulated</em> intensities. After applying the equalization, we get an histogram like the figure in the center. The resulting image is shown in the picture at right.</li>
</ul>
<div class="image">
<img src="../../Histogram_Equalization_Theory_1.jpg" alt="Histogram_Equalization_Theory_1.jpg"/>
</div>
<h3>How does it work?</h3>
<ul>
<li>Equalization implies <em>mapping</em> one distribution (the given histogram) to another distribution (a wider and more uniform distribution of intensity values) so the intensity values are spread over the whole range.</li>
<li><p class="startli">To accomplish the equalization effect, the remapping should be the <em>cumulative distribution function (cdf)</em> (more details, refer to <em>Learning OpenCV</em>). For the histogram \(H(i)\), its <em>cumulative distribution</em> \(H^{&#39;}(i)\) is:</p>
<p class="formulaDsp">
\[H^{&#39;}(i) = \sum_{0 \le j &lt; i} H(j)\]
</p>
<p class="startli">To use this as a remapping function, we have to normalize \(H^{&#39;}(i)\) such that the maximum value is 255 ( or the maximum value for the intensity of the image ). From the example above, the cumulative function is:</p>
<div class="image">
<img src="../../Histogram_Equalization_Theory_2.jpg" alt="Histogram_Equalization_Theory_2.jpg"/>
</div>
</li>
<li><p class="startli">Finally, we use a simple remapping procedure to obtain the intensity values of the equalized image:</p>
<p class="formulaDsp">
\[equalized( x, y ) = H^{&#39;}( src(x,y) )\]
</p>
</li>
</ul>
<h2>Code </h2>
<ul>
<li><b>What does this program do?</b><ul>
<li>Loads an image</li>
<li>Convert the original image to grayscale</li>
<li>Equalize the Histogram by using the OpenCV function <a class="el" href="../../d6/dc7/group__imgproc__hist.html#ga7e54091f0c937d49bf84152a16f76d6e">cv::equalizeHist</a></li>
<li>Display the source and equalized images in a window.</li>
</ul>
</li>
</ul>
 <div class='newInnerHTML' title='cpp' style='display: none;'>C++</div><div class='toggleable_div label_cpp' style='display: none;'><ul>
<li><b>Downloadable code</b>: Click <a href="https://github.com/opencv/opencv/tree/master/samples/cpp/tutorial_code/Histograms_Matching/EqualizeHist_Demo.cpp">here</a></li>
<li><b>Code at glance:</b> <div class="fragment"><div class="line"></div><div class="line"><span class="preprocessor">#include &quot;<a class="code" href="../../d6/d87/imgcodecs_8hpp.html">opencv2/imgcodecs.hpp</a>&quot;</span></div><div class="line"><span class="preprocessor">#include &quot;<a class="code" href="../../d4/dd5/highgui_8hpp.html">opencv2/highgui.hpp</a>&quot;</span></div><div class="line"><span class="preprocessor">#include &quot;<a class="code" href="../../d1/d4f/imgproc_2include_2opencv2_2imgproc_8hpp.html">opencv2/imgproc.hpp</a>&quot;</span></div><div class="line"><span class="preprocessor">#include &lt;iostream&gt;</span></div><div class="line"></div><div class="line"><span class="keyword">using namespace </span><a class="code" href="../../d2/d75/namespacecv.html">cv</a>;</div><div class="line"><span class="keyword">using namespace </span>std;</div><div class="line"></div><div class="line"><span class="keywordtype">int</span> main( <span class="keywordtype">int</span> argc, <span class="keywordtype">char</span>** argv )</div><div class="line">{</div><div class="line">    <a class="code" href="../../d0/d2e/classcv_1_1CommandLineParser.html">CommandLineParser</a> parser( argc, argv, <span class="stringliteral">&quot;{@input | lena.jpg | input image}&quot;</span> );</div><div class="line">    <a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a> src = <a class="code" href="../../d4/da8/group__imgcodecs.html#ga288b8b3da0892bd651fce07b3bbd3a56">imread</a>( <a class="code" href="../../d6/dba/group__core__utils__samples.html#ga3a33b00033b46c698ff6340d95569c13">samples::findFile</a>( parser.get&lt;<a class="code" href="../../dc/d84/group__core__basic.html#ga1f6634802eeadfd7245bc75cf3e216c2">String</a>&gt;( <span class="stringliteral">&quot;@input&quot;</span> ) ), <a class="code" href="../../d8/d6a/group__imgcodecs__flags.html#gga61d9b0126a3e57d9277ac48327799c80af660544735200cbe942eea09232eb822">IMREAD_COLOR</a> );</div><div class="line">    <span class="keywordflow">if</span>( src.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#abbec3525a852e77998aba034813fded4">empty</a>() )</div><div class="line">    {</div><div class="line">        cout &lt;&lt; <span class="stringliteral">&quot;Could not open or find the image!\n&quot;</span> &lt;&lt; endl;</div><div class="line">        cout &lt;&lt; <span class="stringliteral">&quot;Usage: &quot;</span> &lt;&lt; argv[0] &lt;&lt; <span class="stringliteral">&quot; &lt;Input image&gt;&quot;</span> &lt;&lt; endl;</div><div class="line">        <span class="keywordflow">return</span> -1;</div><div class="line">    }</div><div class="line"></div><div class="line">    <a class="code" href="../../d8/d01/group__imgproc__color__conversions.html#ga397ae87e1288a81d2363b61574eb8cab">cvtColor</a>( src, src, <a class="code" href="../../d8/d01/group__imgproc__color__conversions.html#gga4e0972be5de079fed4e3a10e24ef5ef0a353a4b8db9040165db4dacb5bcefb6ea">COLOR_BGR2GRAY</a> );</div><div class="line"></div><div class="line">    <a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a> dst;</div><div class="line">    <a class="code" href="../../d6/dc7/group__imgproc__hist.html#ga7e54091f0c937d49bf84152a16f76d6e">equalizeHist</a>( src, dst );</div><div class="line"></div><div class="line">    <a class="code" href="../../d7/dfc/group__highgui.html#ga453d42fe4cb60e5723281a89973ee563">imshow</a>( <span class="stringliteral">&quot;Source image&quot;</span>, src );</div><div class="line">    <a class="code" href="../../d7/dfc/group__highgui.html#ga453d42fe4cb60e5723281a89973ee563">imshow</a>( <span class="stringliteral">&quot;Equalized Image&quot;</span>, dst );</div><div class="line"></div><div class="line">    <a class="code" href="../../d7/dfc/group__highgui.html#ga5628525ad33f52eab17feebcfba38bd7">waitKey</a>();</div><div class="line"></div><div class="line">    <span class="keywordflow">return</span> 0;</div><div class="line"></div><div class="line">}</div></div><!-- fragment -->  </div> </li>
</ul>
 <div class='newInnerHTML' title='java' style='display: none;'>Java</div><div class='toggleable_div label_java' style='display: none;'><ul>
<li><b>Downloadable code</b>: Click <a href="https://github.com/opencv/opencv/tree/master/samples/java/tutorial_code/Histograms_Matching/histogram_equalization/EqualizeHistDemo.java">here</a></li>
<li><b>Code at glance:</b> <div class="fragment"><div class="line"><span class="keyword">import</span> org.opencv.core.Core;</div><div class="line"><span class="keyword">import</span> org.opencv.core.Mat;</div><div class="line"><span class="keyword">import</span> org.opencv.highgui.HighGui;</div><div class="line"><span class="keyword">import</span> org.opencv.imgcodecs.Imgcodecs;</div><div class="line"><span class="keyword">import</span> org.opencv.imgproc.Imgproc;</div><div class="line"></div><div class="line"><span class="keyword">class </span>EqualizeHist {</div><div class="line">    <span class="keyword">public</span> <span class="keywordtype">void</span> run(<a class="code" href="../../dc/d84/group__core__basic.html#ga1f6634802eeadfd7245bc75cf3e216c2">String</a>[] args) {</div><div class="line">        <a class="code" href="../../dc/d84/group__core__basic.html#ga1f6634802eeadfd7245bc75cf3e216c2">String</a> filename = args.length &gt; 0 ? args[0] : <span class="stringliteral">&quot;../data/lena.jpg&quot;</span>;</div><div class="line">        Mat src = Imgcodecs.imread(filename);</div><div class="line">        <span class="keywordflow">if</span> (src.empty()) {</div><div class="line">            System.err.println(<span class="stringliteral">&quot;Cannot read image: &quot;</span> + filename);</div><div class="line">            System.exit(0);</div><div class="line">        }</div><div class="line"></div><div class="line">        Imgproc.cvtColor(src, src, Imgproc.COLOR_BGR2GRAY);</div><div class="line"></div><div class="line">        Mat dst = <span class="keyword">new</span> Mat();</div><div class="line">        Imgproc.equalizeHist( src, dst );</div><div class="line"></div><div class="line">        HighGui.imshow( <span class="stringliteral">&quot;Source image&quot;</span>, src );</div><div class="line">        HighGui.imshow( <span class="stringliteral">&quot;Equalized Image&quot;</span>, dst );</div><div class="line"></div><div class="line">        HighGui.waitKey(0);</div><div class="line"></div><div class="line">        System.exit(0);</div><div class="line">    }</div><div class="line">}</div><div class="line"></div><div class="line"><span class="keyword">public</span> <span class="keyword">class </span>EqualizeHistDemo {</div><div class="line"></div><div class="line">    <span class="keyword">public</span> <span class="keyword">static</span> <span class="keywordtype">void</span> main(<a class="code" href="../../dc/d84/group__core__basic.html#ga1f6634802eeadfd7245bc75cf3e216c2">String</a>[] args) {</div><div class="line">        <span class="comment">// Load the native OpenCV library</span></div><div class="line">        System.loadLibrary(Core.NATIVE_LIBRARY_NAME);</div><div class="line"></div><div class="line">        <span class="keyword">new</span> EqualizeHist().run(args);</div><div class="line">    }</div><div class="line"></div><div class="line">}</div></div><!-- fragment -->  </div> </li>
</ul>
 <div class='newInnerHTML' title='python' style='display: none;'>Python</div><div class='toggleable_div label_python' style='display: none;'><ul>
<li><b>Downloadable code</b>: Click <a href="https://github.com/opencv/opencv/tree/master/samples/python/tutorial_code/Histograms_Matching/histogram_equalization/EqualizeHist_Demo.py">here</a></li>
<li><b>Code at glance:</b> <div class="fragment"><div class="line"><span class="keyword">from</span> __future__ <span class="keyword">import</span> print_function</div><div class="line"><span class="keyword">import</span> cv2 <span class="keyword">as</span> cv</div><div class="line"><span class="keyword">import</span> argparse</div><div class="line"></div><div class="line"></div><div class="line">parser = argparse.ArgumentParser(description=<span class="stringliteral">&#39;Code for Histogram Equalization tutorial.&#39;</span>)</div><div class="line">parser.add_argument(<span class="stringliteral">&#39;--input&#39;</span>, help=<span class="stringliteral">&#39;Path to input image.&#39;</span>, default=<span class="stringliteral">&#39;lena.jpg&#39;</span>)</div><div class="line">args = parser.parse_args()</div><div class="line"></div><div class="line">src = <a class="code" href="../../d4/da8/group__imgcodecs.html#ga288b8b3da0892bd651fce07b3bbd3a56">cv.imread</a>(<a class="code" href="../../d6/dba/group__core__utils__samples.html#ga3a33b00033b46c698ff6340d95569c13">cv.samples.findFile</a>(args.input))</div><div class="line"><span class="keywordflow">if</span> src <span class="keywordflow">is</span> <span class="keywordtype">None</span>:</div><div class="line">    <a class="code" href="../../df/d57/namespacecv_1_1dnn.html#a701210a0203f2786cbfd04b2bd56da47">print</a>(<span class="stringliteral">&#39;Could not open or find the image:&#39;</span>, args.input)</div><div class="line">    exit(0)</div><div class="line"></div><div class="line"></div><div class="line"></div><div class="line">src = <a class="code" href="../../d8/d01/group__imgproc__color__conversions.html#ga397ae87e1288a81d2363b61574eb8cab">cv.cvtColor</a>(src, cv.COLOR_BGR2GRAY)</div><div class="line"></div><div class="line"></div><div class="line"></div><div class="line">dst = <a class="code" href="../../d6/dc7/group__imgproc__hist.html#ga7e54091f0c937d49bf84152a16f76d6e">cv.equalizeHist</a>(src)</div><div class="line"></div><div class="line"></div><div class="line"></div><div class="line"><a class="code" href="../../df/d24/group__highgui__opengl.html#gaae7e90aa3415c68dba22a5ff2cefc25d">cv.imshow</a>(<span class="stringliteral">&#39;Source image&#39;</span>, src)</div><div class="line"><a class="code" href="../../df/d24/group__highgui__opengl.html#gaae7e90aa3415c68dba22a5ff2cefc25d">cv.imshow</a>(<span class="stringliteral">&#39;Equalized Image&#39;</span>, dst)</div><div class="line"></div><div class="line"></div><div class="line"></div><div class="line"><a class="code" href="../../d7/dfc/group__highgui.html#ga5628525ad33f52eab17feebcfba38bd7">cv.waitKey</a>()</div><div class="line"></div></div><!-- fragment -->  </div> </li>
</ul>
<h2>Explanation </h2>
<ul>
<li>Load the source image:</li>
</ul>
 <div class='newInnerHTML' title='cpp' style='display: none;'>C++</div><div class='toggleable_div label_cpp' style='display: none;'> <div class="fragment"><div class="line">    CommandLineParser parser( argc, argv, <span class="stringliteral">&quot;{@input | lena.jpg | input image}&quot;</span> );</div><div class="line">    Mat src = <a class="code" href="../../d4/da8/group__imgcodecs.html#ga288b8b3da0892bd651fce07b3bbd3a56">imread</a>( <a class="code" href="../../d6/dba/group__core__utils__samples.html#ga3a33b00033b46c698ff6340d95569c13">samples::findFile</a>( parser.get&lt;<a class="code" href="../../dc/d84/group__core__basic.html#ga1f6634802eeadfd7245bc75cf3e216c2">String</a>&gt;( <span class="stringliteral">&quot;@input&quot;</span> ) ), <a class="code" href="../../d8/d6a/group__imgcodecs__flags.html#gga61d9b0126a3e57d9277ac48327799c80af660544735200cbe942eea09232eb822">IMREAD_COLOR</a> );</div><div class="line">    <span class="keywordflow">if</span>( src.empty() )</div><div class="line">    {</div><div class="line">        cout &lt;&lt; <span class="stringliteral">&quot;Could not open or find the image!\n&quot;</span> &lt;&lt; endl;</div><div class="line">        cout &lt;&lt; <span class="stringliteral">&quot;Usage: &quot;</span> &lt;&lt; argv[0] &lt;&lt; <span class="stringliteral">&quot; &lt;Input image&gt;&quot;</span> &lt;&lt; endl;</div><div class="line">        <span class="keywordflow">return</span> -1;</div><div class="line">    }</div></div><!-- fragment --> </div>  <div class='newInnerHTML' title='java' style='display: none;'>Java</div><div class='toggleable_div label_java' style='display: none;'> <div class="fragment"><div class="line">        <a class="code" href="../../dc/d84/group__core__basic.html#ga1f6634802eeadfd7245bc75cf3e216c2">String</a> filename = args.length &gt; 0 ? args[0] : <span class="stringliteral">&quot;../data/lena.jpg&quot;</span>;</div><div class="line">        Mat src = Imgcodecs.imread(filename);</div><div class="line">        <span class="keywordflow">if</span> (src.empty()) {</div><div class="line">            System.err.println(<span class="stringliteral">&quot;Cannot read image: &quot;</span> + filename);</div><div class="line">            System.exit(0);</div><div class="line">        }</div></div><!-- fragment --> </div>  <div class='newInnerHTML' title='python' style='display: none;'>Python</div><div class='toggleable_div label_python' style='display: none;'> <div class="fragment"><div class="line">parser = argparse.ArgumentParser(description=<span class="stringliteral">&#39;Code for Histogram Equalization tutorial.&#39;</span>)</div><div class="line">parser.add_argument(<span class="stringliteral">&#39;--input&#39;</span>, help=<span class="stringliteral">&#39;Path to input image.&#39;</span>, default=<span class="stringliteral">&#39;lena.jpg&#39;</span>)</div><div class="line">args = parser.parse_args()</div><div class="line"></div><div class="line">src = <a class="code" href="../../d4/da8/group__imgcodecs.html#ga288b8b3da0892bd651fce07b3bbd3a56">cv.imread</a>(<a class="code" href="../../d6/dba/group__core__utils__samples.html#ga3a33b00033b46c698ff6340d95569c13">cv.samples.findFile</a>(args.input))</div><div class="line"><span class="keywordflow">if</span> src <span class="keywordflow">is</span> <span class="keywordtype">None</span>:</div><div class="line">    <a class="code" href="../../df/d57/namespacecv_1_1dnn.html#a701210a0203f2786cbfd04b2bd56da47">print</a>(<span class="stringliteral">&#39;Could not open or find the image:&#39;</span>, args.input)</div><div class="line">    exit(0)</div></div><!-- fragment --> </div> <ul>
<li>Convert it to grayscale:</li>
</ul>
 <div class='newInnerHTML' title='cpp' style='display: none;'>C++</div><div class='toggleable_div label_cpp' style='display: none;'> <div class="fragment"><div class="line">    <a class="code" href="../../d8/d01/group__imgproc__color__conversions.html#ga397ae87e1288a81d2363b61574eb8cab">cvtColor</a>( src, src, <a class="code" href="../../d8/d01/group__imgproc__color__conversions.html#gga4e0972be5de079fed4e3a10e24ef5ef0a353a4b8db9040165db4dacb5bcefb6ea">COLOR_BGR2GRAY</a> );</div></div><!-- fragment --> </div>  <div class='newInnerHTML' title='java' style='display: none;'>Java</div><div class='toggleable_div label_java' style='display: none;'> <div class="fragment"><div class="line">        Imgproc.cvtColor(src, src, Imgproc.COLOR_BGR2GRAY);</div></div><!-- fragment --> </div>  <div class='newInnerHTML' title='python' style='display: none;'>Python</div><div class='toggleable_div label_python' style='display: none;'> <div class="fragment"><div class="line">src = <a class="code" href="../../d8/d01/group__imgproc__color__conversions.html#ga397ae87e1288a81d2363b61574eb8cab">cv.cvtColor</a>(src, cv.COLOR_BGR2GRAY)</div></div><!-- fragment --> </div> <ul>
<li>Apply histogram equalization with the function <a class="el" href="../../d6/dc7/group__imgproc__hist.html#ga7e54091f0c937d49bf84152a16f76d6e">cv::equalizeHist</a> :</li>
</ul>
 <div class='newInnerHTML' title='cpp' style='display: none;'>C++</div><div class='toggleable_div label_cpp' style='display: none;'> <div class="fragment"><div class="line">    Mat dst;</div><div class="line">    <a class="code" href="../../d6/dc7/group__imgproc__hist.html#ga7e54091f0c937d49bf84152a16f76d6e">equalizeHist</a>( src, dst );</div></div><!-- fragment --> </div>  <div class='newInnerHTML' title='java' style='display: none;'>Java</div><div class='toggleable_div label_java' style='display: none;'> <div class="fragment"><div class="line">        Mat dst = <span class="keyword">new</span> Mat();</div><div class="line">        Imgproc.equalizeHist( src, dst );</div></div><!-- fragment --> </div>  <div class='newInnerHTML' title='python' style='display: none;'>Python</div><div class='toggleable_div label_python' style='display: none;'> <div class="fragment"><div class="line">dst = <a class="code" href="../../d6/dc7/group__imgproc__hist.html#ga7e54091f0c937d49bf84152a16f76d6e">cv.equalizeHist</a>(src)</div></div><!-- fragment --> </div> <p> As it can be easily seen, the only arguments are the original image and the output (equalized) image.</p>
<ul>
<li>Display both images (original and equalized):</li>
</ul>
 <div class='newInnerHTML' title='cpp' style='display: none;'>C++</div><div class='toggleable_div label_cpp' style='display: none;'> <div class="fragment"><div class="line">    <a class="code" href="../../d7/dfc/group__highgui.html#ga453d42fe4cb60e5723281a89973ee563">imshow</a>( <span class="stringliteral">&quot;Source image&quot;</span>, src );</div><div class="line">    <a class="code" href="../../d7/dfc/group__highgui.html#ga453d42fe4cb60e5723281a89973ee563">imshow</a>( <span class="stringliteral">&quot;Equalized Image&quot;</span>, dst );</div></div><!-- fragment --> </div>  <div class='newInnerHTML' title='java' style='display: none;'>Java</div><div class='toggleable_div label_java' style='display: none;'> <div class="fragment"><div class="line">        HighGui.imshow( <span class="stringliteral">&quot;Source image&quot;</span>, src );</div><div class="line">        HighGui.imshow( <span class="stringliteral">&quot;Equalized Image&quot;</span>, dst );</div></div><!-- fragment --> </div>  <div class='newInnerHTML' title='python' style='display: none;'>Python</div><div class='toggleable_div label_python' style='display: none;'> <div class="fragment"><div class="line"><a class="code" href="../../df/d24/group__highgui__opengl.html#gaae7e90aa3415c68dba22a5ff2cefc25d">cv.imshow</a>(<span class="stringliteral">&#39;Source image&#39;</span>, src)</div><div class="line"><a class="code" href="../../df/d24/group__highgui__opengl.html#gaae7e90aa3415c68dba22a5ff2cefc25d">cv.imshow</a>(<span class="stringliteral">&#39;Equalized Image&#39;</span>, dst)</div></div><!-- fragment --> </div> <ul>
<li>Wait until user exists the program</li>
</ul>
 <div class='newInnerHTML' title='cpp' style='display: none;'>C++</div><div class='toggleable_div label_cpp' style='display: none;'> <div class="fragment"><div class="line">    <a class="code" href="../../d7/dfc/group__highgui.html#ga5628525ad33f52eab17feebcfba38bd7">waitKey</a>();</div></div><!-- fragment --> </div>  <div class='newInnerHTML' title='java' style='display: none;'>Java</div><div class='toggleable_div label_java' style='display: none;'> <div class="fragment"><div class="line">        HighGui.waitKey(0);</div></div><!-- fragment --> </div>  <div class='newInnerHTML' title='python' style='display: none;'>Python</div><div class='toggleable_div label_python' style='display: none;'> <div class="fragment"><div class="line"><a class="code" href="../../d7/dfc/group__highgui.html#ga5628525ad33f52eab17feebcfba38bd7">cv.waitKey</a>()</div></div><!-- fragment --> </div> <h2>Results </h2>
<ol type="1">
<li><p class="startli">To appreciate better the results of equalization, let's introduce an image with not much contrast, such as:</p>
<div class="image">
<img src="../../Histogram_Equalization_Original_Image.jpg" alt="Histogram_Equalization_Original_Image.jpg"/>
</div>
<p class="startli">which, by the way, has this histogram:</p>
<div class="image">
<img src="../../Histogram_Equalization_Original_Histogram.jpg" alt="Histogram_Equalization_Original_Histogram.jpg"/>
</div>
<p class="startli">notice that the pixels are clustered around the center of the histogram.</p>
</li>
<li><p class="startli">After applying the equalization with our program, we get this result:</p>
<div class="image">
<img src="../../Histogram_Equalization_Equalized_Image.jpg" alt="Histogram_Equalization_Equalized_Image.jpg"/>
</div>
<p class="startli">this image has certainly more contrast. Check out its new histogram like this:</p>
<div class="image">
<img src="../../Histogram_Equalization_Equalized_Histogram.jpg" alt="Histogram_Equalization_Equalized_Histogram.jpg"/>
</div>
<p class="startli">Notice how the number of pixels is more distributed through the intensity range.</p>
</li>
</ol>
<dl class="section note"><dt>Note</dt><dd>Are you wondering how did we draw the Histogram figures shown above? Check out the following tutorial! </dd></dl>
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